The present invention relates generally to non-contact measurement methods and an apparatus for the identification of hazardous contact voltages on energized objects and surfaces proximate to electric power sources or conductors.
Each year, many animals and people suffer “electric shocks” on energized metallic objects from several sources of electric potential. Some of these “electric shocks” have previously proven to be lethal to both animals and people. Electric utilities are responsible for the distribution and transmission of electric power to homes and businesses and hence have been found responsible to identify and mitigate these potentially lethal voltage sources. Previously some devices have been available to provide a warning, but with higher than wanted “false positive” warnings. The false warnings take valuable manpower away from the identification and mitigation of truly life threatening voltage points.
During a typical utility company evaluation of a “shock” complaint about contact voltage, the investigator must be cognizant of the fact that the source of the shock is initially undefined but could be caused by many possible sources. As the voltage magnitude is unknown, the investigator must not contact the source for safety reasons. These contact points encompass a variety of voltage and current sources and include but are not limited to faulted electrical equipment, such as motors, water heaters, and so on where the breaker has not opened; inadvertent energization of a conductive object, such as service boxes, streetlights, manholes, etc; electric field coupling such as the electric field from an overhead power line coupling voltage to a metal casing of a streetlight or other conductive object proximate to the electric field; neutral conductor voltage drop, such as current flow through neutral resistance or the I×R drop; harmonic resonance, such as power system currents interacting with the circuit elements where the harmonic voltages are related to the power line frequency; and magnetic induction, such as current on a power line conductor inducing voltage on a parallel pipeline, fence, or conductor proximate to the power line conductor.
While only the first two of the enumerated conditions warrant immediate attention, initial evaluation precautions assume that an electric shock hazard is present unless metering equipment provides an indication via measured voltage levels that it is not an electric shock hazard. If an electrical hazard is present, it is important to secure the area with warning or caution barriers such that humans and animals are unlikely to contact the energized object(s) until they can be de-energized and repaired.
The second precaution is to consider that the level of voltage present either on an energized object or at a neutral-to-ground bonding point will vary with season, circuit loading, intermittent contact of a faulted conductor, and in some reports, the photo sensors in street lighting systems. When a shock complaint is received, there is a chance that no contact voltage situations will be found on the first try, so the complaint area may require a more thorough investigation to determine the possibility of an intermittent problem.